Semiconductor wafer and manufacturing method thereof

ABSTRACT

The present invention provides a semiconductor wafer comprising an insulated board of sapphire or the like having translucency, which is provided with a positioning orientation flat at a peripheral portion thereof, and a silicon thin film formed over the entire one surface of the insulated board. In the semiconductor wafer, ions are implanted in an area containing the orientation flat at a peripheral portion of the silicon thin film to amorphize silicon. Thus, the translucency at the amorphized spot is eliminated and accurate positioning using the conventional optical sensor can be performed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor wafer in which asilicon thin film is formed over the surface of a transparent insulatedboard, like SOS (Silicon on Sapphire) or the like, and a method ofmanufacturing the semiconductor wafer.

2. Description of the Related Art

In a wafer process for manufacture of a semiconductor device, apositioning orientation flat is previously provided at one point on thecircumference of a disk type semiconductor wafer. A stage with thesemiconductor wafer mounted thereon is rotated and the orientation flatis detected by a photosensor or optical sensor using visible light(e.g., laser light having a wavelength of 633 nm), thereby performing,accurate positioning of the semiconductor wafer. In the case of asilicon wafer using a general silicon substrate, the thickness of thesilicon substrate is greater than or equal to a predetermined thickness.Therefore, an orientation flat and spots other than it are different inlight transmittance and hence the positioning of the silicon wafer canbe performed easily.

Each of SOS and SOQ (Silicon on Quartz) processes has recently been usedwherein a silicon thin film is formed over the surface of an insulatedboard of sapphire or quartz or the like, and an integrated circuit isformed over the silicon thin film. Since SOS and SOQ make use of theinsulated board respectively, no leak current flows in a substrate likethe silicon substrate and a reduction in power consumption is enabled.Therefore, each of SOS and SOQ has come to attention as a semiconductordevice built in a portable type device in particular.

Since, however, the sapphire and quartz are high in light transmittanceand a silicon thin film formed over its surface is also high in lighttransmittance because it becomes a monocrystal having a thickness of 1μm or less, for example. Thus, it is not possible to detect anorientation flat by using the conventional optical sensor in a state ofbeing kept intact.

Therefore, a patent document 1 (Japanese Unexamined Patent PublicationNo. Hei 11(1999) -220114) discloses a method of manufacturing asemiconductor device, wherein a silicon thin film for formation ofcircuit elements is formed over the surface of a sapphire substrate, anda light-penetration preventing polysilicon thick film is formed over itsback, respectively, and an orientation flat is provided at the entiresurface of the polysilicon thick film on the back, thereby preventingwarpage and cracks of the substrate.

Further, a patent document 2 (Japanese Unexamined Patent Publication No.2000-36585) discloses a method of manufacturing a semiconductor device,wherein in order to prevent warpage and cracks of a substrate due to asilicon thick film, a silicon thin film is formed on the obverse andreverse sides of a sapphire substrate, and silicon ions are implanted inthe silicon thin film placed over the back thereof to amorphize theentire silicon thin film placed over the back, thereby forming alight-penetration preventing film.

As disclosed in, for example, the patent document 2, however, theconventional manufacturing method of semiconductor device needs to forma silicon oxide film over the silicon thin film placed over the surfaceof the sapphire substrate for the purpose of protection of the siliconthin film placed over the surface thereof before the implantation of theions in the silicon thin film placed over the back thereof, and furtherto remove the silicon oxide film for the purpose of circuit formationafter the ion implantation. It is also necessary to remove thelight-penetration preventing film placed over the back after thecompletion of formation of the semiconductor device with respect to thesilicon thin film placed over the surface. Thus, complex process stepswere needed to form the light-penetration preventing film over the back.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductorwafer such as SOS, SOQ, etc., which can be simplified in manufacturingprocess and which produces no warpage and cracks in a wafer process andcan be accurately positioned by an optical sensor, and a method ofmanufacturing the semiconductor wafer.

According to one aspect of the present invention, for achieving theobject, there is provided a semiconductor wafer comprising an insulatedboard having a light-penetrating property, which is provided with apositioning orientation flat at a peripheral portion thereof, and asilicon thin film formed over the entire one surface of the insulatedboard, wherein silicon of the peripheral portion containing theorientation flat is amorphized within the silicon thin film.

According to another aspect of the invention, for achieving the object,there is provided a method of manufacturing a semiconductor wafer,comprising the steps of forming a silicon thin film over the entire onesurface of an insulated board having a light-penetrating property, whichis provided with a positioning orientation flat at a peripheral portionthereof, covering a central portion containing a device forming area ofthe silicon thin film with a resist mask, effecting ion implantation onan area for the peripheral portion containing the orientation flat ofthe insulated board within the silicon thin film, using the resist maskto thereby amorphize silicon in the area, and removing the resist maskafter the ion implantation, wherein the respective steps are performedsequentially.

Since the amorphized silicon thin film is formed in the correspondingarea provided with the positioning orientation flat at the peripheralportion of the semiconductor wafer in the present invention, thetransparency of visible light is eliminated at the peripheral portion.Thus, even in the case of a light-transmitting semiconductor wafer likeSOS or SOQ, an orientation flat is detected by an optical sensor toenable its precise positioning.

Since the semiconductor wafer of the present invention needs not have alight-penetration preventing film like a polysilicon thick film over itsback, warpage and cracks in a wafer processing step do not occur, sothat a high reliable semiconductor device can be formed.

Further, the method of manufacturing the semiconductor wafer accordingto the present invention forms the silicon thin film over one surface ofthe insulated board, covers the central portion of the silicon thin filmwith the resist mask, and effects ion implantation on the peripheralportion by use of the resist mask. Therefore, it is possible to form thesemiconductor wafer by processing of only one surface of the insulatedboard. Thus, a manufacturing process can be simplified significantly ascompared with the conventional manufacturing method which effectsprocessing on both surfaces of the insulated board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-1B are configurational views of a semiconductor wafer showing afirst embodiment of the present invention;

FIG. 2A-2D are process views showing a method of manufacturing thesemiconductor wafer shown in FIG. 1A-1B;

FIG. 3 is a cross-sectional view of a semiconductor wafer illustrating asecond embodiment of the present invention; and

FIG. 4A-4C are cross-sectional views for describing a process formanufacturing a semiconductor wafer showing a third embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A semiconductor wafer comprises an insulated board having alight-penetrating property, which is provided with a positioningorientation flat at a peripheral portion thereof, a silicon thin filmformed over the entire one surface of the insulated board, and a siliconfilm having a rough surface formed over the entire surface of theinsulated board, which is located on the opposite side of the siliconthin film. Such a semiconductor wafer can be manufactured by forming asilicon thin film and an oxide silicon film over the entire surface ofan insulated board, forming an amorphized silicon film over the entireback thereof, effecting HSG (hemispherical grain) processing on thesurface of the silicon film, and thereafter removing the oxide siliconfilm to expose the silicon thin film.

The above and other objects and novel features of the present inventionwill become more completely apparent from the following descriptions ofpreferred embodiments when the same is read with reference to theaccompanying drawings. The drawings, however, are for the purpose ofillustration only and by no means limitative of the invention.

First Preferred Embodiment

FIG. 1A-1B are configurational views of a semiconductor wafer showing afirst embodiment of the present invention, wherein FIG. 1A is a planview thereof and FIG. 1B is a cross-sectional view thereof respectively.

The present semiconductor wafer comprises a disk type sapphire substrate1 provided with a positioning orientation flag (OF) at one point on itscircumference, and a silicon thin film 2 formed over the entire surfaceof the sapphire substrate 1. The silicon thin film 2 is divided into aninner ring portion 2 a reduced in diameter by about 10 mm from thediameter of the sapphire substrate 1, and an outer ring portion 2 bhaving a width of about 5 mm, which extends along its outercircumference.

The inner ring portion 2 a of the silicon thin film 2 is constituted ofa crystalline silicon layer and equivalent to a portion which serves asa device forming area. The outer ring portion 2 b corresponds to apositioning area formed of a silicon layer amorphized and low inlight-penetrating property. The orientation flat OF is defined in theouter ring portion 2 b so as not to extend to the inner ring portion 2a.

FIG. 2A-2D are process views showing a method of manufacturing thesemiconductor wafer shown in FIG. 1A-1B. The manufacturing method of thesemiconductor wafer shown in FIG. 1A-1B will be explained below withreference to FIG. 2A-2D.

(1) Process 1 (FIG. 2A)

A disk type sapphire substrate 1 provided with an orientation flat OF isprepared. A silicon thin film 2 having a thickness ranging fromapproximately 20 to 200 nm is formed over the entire surface of thesapphire substrate 1 by, for example, epitaxial growth.

(2) Process 2 (FIG. 2B)

A resist agent 3, which serves as a mask at ion implantation, is appliedonto the surface of the silicon thin film 2. Further, the resist agent 3at the outer peripheral portion of the substrate is removed using, forexample, photolithography with an effective device area lying in thesubstrate left behind. The width of the resist agent 3 to be removed isdetermined by the allowable range of a wafer position sensor of a deviceused for wafer processing and the effective device area lying in thesubstrate. However, the width thereof needs at least the maximum notchsize (e.g., about 5 mm) or more of the orientation flat (OF).

(3) Process 3 (FIG. 2C)

The implantation of ions is effected to amorphize the substrate outerperipheral portion of the silicon thin film 2 with the resist agent 3from which the substrate outer peripheral portion has been removed, asthe mask. Although the conditions for the ion implantation needs not tobe strict in particular, an ion species is set to silicon, energy is setto 160 keV and the amount of dose is set to 5×10¹⁴/cm². Incidentally,the ion species aims to collapse crystalline and is regardless of thetype. When an oxide film or the like is formed over the silicon layer,the energy and the like are also set to suitable values according to itsthickness so that the ions are capable of reaching the silicon layer.The temperature at the ion implantation may be a heat-resistanttemperature (e.g., 100° C.) or less of the resist agent 3.

(4) Process 4 (FIG. 2D)

After the ion implantation, the resist agent 3 is removed. Thus, thecrystalline silicon remains in the inner ring portion 2 a of the siliconthin film 2 as it is, and the silicon of the outer ring portion 2 b isamorphized so that transparency of visible light becomes low, therebyleading to completion of such a semiconductor wafer as shown in FIG.1A-1B. Incidentally, if the once-amorphized silicon is held at 560° C.or less, then its state is maintained as it is, whereas if thetemperature reaches 560° C. or higher, the silicon is recrystallized andreturns to a transparent state. Thus, when the visible light is set soas to penetrate by high-temperature processing during a wafer processingstep, the ion implantation is done again by a similar method to avoidthe transparency of the visible light.

Thus, the semiconductor wafer according to the first embodiment has thesilicon thin film having the amorphized outer ring portion 2 b in such amanner that the visible light does not pass through the wafer peripheralportion containing the orientation flat OF. Accordingly, the positioningof the semiconductor wafer can be easily performed by searching theorientation flat OF of the outer ring portion 2 b according to a methodsimilar to one for the normal silicon wafer.

The semiconductor wafer has the advantages that since alight-penetration preventing film like a polysilicon thick film is notformed over its back surface, warpage in the wafer processing step canbe reduced and cracks can be eliminated, and hence a high reliablesemiconductor device can be formed.

Further, the semiconductor wafer has the advantage that since it can beformed by processing only the surface of the sapphire substrate 1, themanufacturing process can be simplified by far as compared with theconventional manufacturing method.

Second Preferred Embodiment

FIG. 3 is a cross-sectional view of a semiconductor wafer showing asecond embodiment of the present invention.

The semiconductor wafer includes a disk type sapphire substrate 1provided with a positioning orientation flag (OF) at one point (notshown) on its circumference, and a silicon thin film 4 formed over theentire one surface of the sapphire substrate 1. An oxide silicon film 5is formed over the entire surface of the silicon thin film 4. A siliconfilm having a rough surface, comprising an amorphized silicon film 6 andan HSG polysilicon film (hereinafter called simply “HSG film”) 7, isformed over the entire surface of the sapphire substrate 1 lying on theside opposite to the surface of the sapphire substrate 1 on which thesilicon thin film 4 is formed. The HSG film 7 is of a polysilicon filmwhose surface is roughened by hemispherical polysilicon grains and hasthe characteristic that light is scattered so that its transmittance isextremely reduced (10% or less, for example).

Such a semiconductor wafer can be manufactured in the following manner.

A disk type sapphire substrate 1 provided with an orientation flat OF isfirst prepared. A silicon thin film 4 having a thickness ranging fromapproximately 20 to 200 nm is formed over the entire surface of thesapphire substrate 1 by epitaxial growth, for example. Further, theentire surface of the silicon thin film 4 is oxidized to form an oxidesilicon film 5.

Next, an amorphized silicon film 6 is formed over the entire back of thesapphire substrate 1 by using SiH4 gas at a temperature of 520° C., forexample. Further, HSG processing is effected on the surface of theamorphized silicon film 6 to form an HSG film 7. The HSG processing isdone using SiH4 gas by the UHV-600 type HSG-CVD apparatus made by ASMcorporation under the conditions of a temperature of 560° C. and apressure of 1×10⁻⁵ Pa.

Thus, the HSG film 7 formed with hemispherical polysilicon grains isobtained at the surface of the amorphized silicon film 6. Under theconditions of such a temperature and pressure, the HSG film 7 isselectively formed only on the surface of the amorphized silicon film 6,and no HSG film is formed on the oxide silicon film 5 lying on theopposite side.

Thereafter, the oxide silicon film 5 formed over the surface of thesilicon thin film 4 is removed, and wafer processing for the formationof circuit elements is effected on the exposed silicon thin film 4.

Since the semiconductor wafer according to the second embodiment has theHSG film 7 which allows the transmitted light to be scattered to theback surface of the wafer as described above, the semiconductor wafercan easily be positioned by searching the orientation flat OF accordingto a method similar to one for the normal silicon wafer.

The HSG film 7 has the advantages that since it may be a thin filmbecause the HSG film 7 causes the light to be scattered by thehemispherical polysilicon grains lying on its surface, warpage in awafer processing step can be reduced and cracks can be eliminated,thereby making it possible to form a high reliable semiconductor device.Further, the HSG film 7 has the advantage that there is no fear of theoccurrence of a light-penetrating property in a high-temperature waferprocessing step as distinct from the amorphized silicon film 2 bemployed in the first embodiment.

Third Preferred Embodiment

FIGS. 4A-4C are cross-sectional views for manufacturing a semiconductorwafer showing a third embodiment of the present invention.

As shown in FIG. 4C, the semiconductor wafer has a disk type sapphiresubstrate 1 provided with a positioning orientation flag OF at one point(not shown) on its circumference, a silicon thin film 4 formed over theentire one surface of the sapphire substrate 1, and an oxide siliconfilm 5 formed over the entire surface of the silicon thin film 4.Further, an amorphized silicon film 8 a is formed over the surface ofthe oxide silicon film 5 at a peripheral portion containing theorientation flat OF, and an HSG film 9 is formed over the silicon film 8a.

The semiconductor wafer is formed by the following manufacturing method,for example.

As shown in FIG. 4A, a disk type sapphire substrate 1 provided with anorientation flat OF is first prepared. A silicon thin film 4 having athickness ranging from approximately 20 to 200 nm is formed over theentire surface of the sapphire substrate 1 by epitaxial growth, forexample. Further, the entire surface of the silicon thin film 4 isoxidized to form an oxide silicon film 5. An amorphized silicon film 8is formed over the entire surface of the oxide silicon film 5 using SiH4gas at a temperature of 520° C., for example.

Next, the peripheral portion of the silicon film 8 containing theorientation flat OF of the sapphire substrate 1 is left, and the innersilicon film 8 is removed by a lithography technique and an etchingtechnique. Thus, as shown in FIG. 4B, the amorphized silicon film 8 isleft on the oxide silicon film 5 at the peripheral portion containingthe orientation flat OF.

Further, HSG processing is effected on the surface of the amorphizedsilicon film 8 a to form an HSG film 9. The HSG processing is done usingSiH4 gas by the HSG-CVD apparatus under the conditions of a temperatureof 560° C. and a pressure of 1×10⁻⁵ Pa. Thus, as shown in FIG. 4C, theHSG film 9 formed with hemispherical polysilicon grains is obtained atthe surface of the amorphized silicon film 8 a. Under the conditions ofsuch a temperature and pressure, the HSG film 9 is selectively formedonly on the surface of the amorphized silicon film 8 a, and no HSG filmis formed over the surface of the oxide silicon film 5 locatedthereinside.

Thereafter, the inner oxide silicon film 5 formed with no HSG film 9 isremoved, and wafer processing for the formation of circuit elements iseffected on the exposed silicon thin film 4.

As described above, the semiconductor wafer according to the thirdembodiment is formed with the HSG film 9 for causing visible light to bescattered to the wafer peripheral portion containing the orientationflat OF. Thus, the semiconductor wafer can easily be positioned bysearching the orientation flat OF of the sapphire substrate 1 accordingto a method similar to one for the normal silicon wafer.

Thus, the semiconductor wafer has the advantage that since it can beformed by the processing to be effected only on the surface of thesapphire substrate 1, its manufacturing process can be simplifiedsignificantly as compared with the conventional manufacturing method.Also the semiconductor wafer has the advantages that since alight-penetration preventing film like a polysilicon thick film is notformed over its back surface, warpage in the wafer processing step canbe reduced and cracks can be eliminated, and hence a high reliablesemiconductor device can be formed. Further, the semiconductor wafer hasthe advantage that there is no fear of the occurrence of translucency ina high-temperature wafer processing step as distinct from the amorphizedsilicon film 2 b employed in the first embodiment.

Fourth Preferred Embodiment

Incidentally, the embodiments referred to above can be implemented byvarious changes. For example, the following embodiments are broughtabout as modifications thereof.

(a) Although a description has been made of the SOS based on thesapphire substrate 1, the present invention is similarly applicable evento SOQ based on a quartz substrate.

(b) The conditions such as the illustrated sizes, materials,temperatures, etc. are shown by way of example. They can be suitablychanged depending on applicable conditions.

(c) Although the disk type semiconductor wafer has been described, thepresent invention is not limited to the disk type. The present inventionis similarly applicable even to a semiconductor wafer having apositioning orientation flat at its peripheral portion. In such a case,preferably, a silicon thin film in a device forming area located in thecenter of the semiconductor wafer is crystallized and a silicon thinfilm at a peripheral portion containing the orientation flat is formedto an amorphized state.

(d) The shape of the orientation flat OF provided around thesemiconductor wafer is arbitrary.

(e) A rough-surfaced polysilicon film may be directly formed over theback of the sapphire substrate 1 as an alternative to the silicon film 6and HSG film 7 lying over the back of the sapphire substrate 1 employedin the second embodiment. The rough-surfaced polysilicon film is formedusing, for example, SiH4 gas under the conditions of a temperature of575° C. and a pressure of 650 Pa or so.

Thus, the polysilicon film which is rough in surface and causestransmitted light to be scattered, can be uniformly formed over the backof the sapphire substrate 1.

(f) Although the inner side of the amorphized silicon film 8 is removedand the HSG film 9 is formed over the surface of the silicon film 8 a ofthe remaining peripheral portion in the third embodiment, the HSG film 9is formed over the entire surface of the silicon film 8 and thereafterthe peripheral portion containing the orientation flat OF is left andthe HSG film 9, silicon film 8 and oxide silicon film 5 provided on theinner side may be removed.

(g) In a manner similar to the above (e), a rough-surfaced polysiliconfilm may be provided as an alternative to the silicon film 8 a and HSGfilm 9 employed in the third embodiment.

(h) The conditions and procedures for the HSG processing in the secondand third embodiments are illustrated by way of example. The HSGprocessing can be done under various conditions. For example, a patentdocument 3 describes that as a method of bringing the surface of astacked electrode of a DRAM (stacked memory cell) into HSG form, asubstrate having produced the stacked electrode, is placed under areduced pressure of about 0.13 Pa at a temperature of about 580° C. andsubjected to Si2H6 gas for about 10 minutes, followed by beingcontinuously subjected to an atmosphere of N2 for about 30 minutes underisothermal and isobaric conditions. Further, the patent document 3 showsdata that in the relationship between reflectivity of a formed HSGsurface and the wavelength of light, the reflectivity becomes a minimal5% or so when the wavelength is about 660 nm, whereas when thewavelength is 633 nm, the reflectivity becomes 10% or so.

While the preferred forms of the present invention have been described,it is to be understood that modifications will be apparent to thoseskilled in the art without departing from the spirit of the invention.The scope of the invention is to be determined solely by the followingclaims.

1-10. (canceled)
 11. A method of manufacturing a semiconductor wafer,comprising the steps of: sequentially forming a silicon thin film and anoxide silicon film over the entire one surface of an insulated boardhaving a light-penetrating property, which is provided with apositioning orientation flat at a peripheral portion thereof; forming asilicon film having a rough surface over the entire surface of theinsulated board, which is located on the side opposite to the formedsurface of the silicon thin film, or at a peripheral portion of theoxide silicon film; and removing an exposed portion of the oxide siliconfilm, wherein said steps are sequentially performed.
 12. The methodaccording to claim 11, wherein the insulated board is a sapphiresubstrate.
 13. The method according to claim 11, wherein the siliconfilm having the rough surface is an HSG polysilicon film.